An X-ray tube outputs X-rays by inpinging electrons on a target, and conventionally has been utilized as an X-ray generator such as an X-ray inspection apparatus or the like which is used for nondestructive inspection, non-contact inspection or the like. For a sample of Such X-ray tube, one disclosed in Japanese Unexamined Examined Utility Model Application No. H03-110753 is well known. The X-ray tube described in this publication has a vacuum envelope molded insulating material such as glass or the like in a substantially cylindrical shape. Both end portions of the vacuum envelope are inwardly folded over the overall peripheries thereof, and thus inner cylinder portions extending to the inside of the envelope are formed at both ends of the vacuum envelope. An electron generating unit containing a cathode filament, a focus electrode, etc., are fixed in one inner cylinder portion. Furthermore, a metal tube is fuse-bonded to the other folded portion. A target supporter for supporting a target is fixed to the metal tube. Accordingly, the electron generating unit and the target oppose each other.
Recently, in order to enhance the sharpness and magnification of a radioscopy image shooting by an X-ray inspection apparatus or the like, it has been required to reduce the dimension (diameter) of the X-ray focus point in the X-ray tube to a smaller point. Therefore, needs for a so-called micro-focus X-ray tube which can set the X-ray focus point to an extremely small point has been increasingly grown. In order to set the X-ray focus point to an extremely small point as described above, it is required to mount a target receiving electrons to a vacuum envelope accurately.